Here is an existing request for assignable LFO, gate, and envelope follower (“dynamics”) functions. If implemented as requested–fingers crossed–you would be able to assign the envelope follower to the mix/blend parameter on a splitter or mixer. Or even send an envelope follower to an LFO, where the LFO controls the same mix/blend parameter.
Not sure what your take on external pedals is, but this is something that the Empress Zoia can do easily.